Configurated lamp



July 23, 1963 E. LEMMERS 3,093,945

CONFIGURATED LAMP Filed June 8, 1961 2 Sheets-Sheet 1 INV EN TOR. fagene Zemmm4 H42; Maine y 3, 1963 E. LEMMERS 3,098,945

CONFIGURATED LAMP Filed June 8, 1961 2 Sheets-Sheet 2 INVENTOR. (fuyme [em mead United States Patent 3,098,945 CGNFIGURATED LAMP Eugene Lemmers, Cleveland Heights, Ohio, assignor to General Electric Company, a corporation of New York Filed June 8, 1961, Ser. No. 115,642 5 Claims. ((31. 313-109) This invention relates to highly loaded low pressure mercury vapor discharge lamps of the kind commonly known as configurated fluorescent lamps having elongated tubular envelopes of non-circular cross-section.

Configurated fluorescent lamps have in recent years found wide acceptance particularly in commercial and industrial applications where high levels of illumination are desired. In one form which is sometimes referred to as a double-groove lamp, short sections of groove are provided alternating on opposite sides of the envelope giving it a 'dimpled or crenelated appearance. The grooved portions combined with the merging portions in-"between achieve a high ratio of perimeter to area of cross-section along with a relatively high implosion resistance. This is highly advantageous in resonance radiation lamps such as fluorescent lamps which utilize the resonance radiation of mercury vapor at 2537 A. to excite the internal phosphor coating on the envelope walls to produce visible light. It permits higher loadings and lumen output per unit axial length at a given efiiciency than was formerly possible. Such lamps were first described and are claimed in Patent 2,915,664, Lemmers, Turbular Electric Lamps, and are sold by applicants assignee as Power Groove lamps.

Among the important factors involved in the high lumen efiiciency achieved With a grooved or generally kidney-shaped cross-section is the high electron temperature or speed obtained simultaneously with reduced elastic collision losses due to more rapid diflusion of electrons, mercury ions, and radiation quanta to the bulb walls. For a given lamp length and wattage, the lamp current is less and the lamp voltage is higher than with a lamp of the same perimeter in a circular cross-section, thereby reducing the proportion of both the cathode losses and the ballast losses. Following these principles, the configurated fluorescent lamp has been further improved by the invention described and claimed in Patent 2,950,410, Lemmers et al. according to which the indentations or grooved sections were shortened and more closely spaced and made relatively open, that is with a wide aperture angle, so as to avoid light trapping within the grooves. In addition the wall-to-wall spacing in the merging sections between indentations was made substantially no greater than in the indentations or grooved sections proper to provide a more uniform constriction of the plasma.

An advantageous characteristic of the configurated fluorescent lamp is its inherent or built-in tendency to regulate the mercury vapor pressure. The joining edge walls or rails on either side of the grooves or indentations are cooler in operation than the remainder of the lamp and their temperature rises more slowly with increase in loading. This effect is due in part to internal construction of the plasma at high loadings causing it to draw away from the rails, and in part to external effects which facilitate cooling of the rails. A further improvement in this respect has been provided by the invention described and claimed in Patent 2,973,447, Aicher et al., Grooved Lamp Vapor Pressure Control, according to which the lamp is provided with at least one and preferably two asymmetric grooves or indentations to serve specifically as mercury vapor pressure control centers. The two asymmetric grooves are preferably located near the longitudinal center of the lamp and in them the groove is deeper and the rail portion on one side of the groove is wider than on the other. The discharge plasma then displaces ice itself towards the wider rail side and away from the narrower rail side. The narrower rails thus operate at a lower temperature than the remainder of the envelope. The narrower rail portion is more effectively cooled by convection flow of air when it is located lowermost. In order to have a non-polarized lamp for mounting with the grooves or indentations facing the sides and which can be rotated at will in either direction, the two asymmetric grooves are offset in opposite directions relative to the diametral medial plane through the ordinary or symmetric grooves. This provides a pair of narrower rail portions on diametrically opposite sides of the lamp so that one of the pair is always located lowermost and that one serves as the effective mercury vapor pressure control menter.

The object of the invention is to provide further improvements and refinements in configurated fluorescent lamps of the double groove type.

Among the features and improvements provided by the present invention are improved vapor pressure control under adverse ambient conditions, as in an environment subject to drafts and to rapid changes in temperature, and more rapid stabilization of mercury vapor pressure after a period of non-operation. Additional features are an improvement in lumen maintenance and an increase in loading capacity which may in the alternative be taken advantage of as a decrease in starting voltage for the same loading.

As mentioned above, it was previously known to be desirable to provide at least one and preferably two asymmetric grooves for the specific purpose of serving as a Vapor pressure control center. I have now discovered that there are very decided and unexpected advantages in making all the grooves or indentations so to speak asymmetric. Therefore in accordance with the present invention all or at least a substantial block of the grooves on one side of the diametral plane through the lamp are olfset laterally in one direction whereas the corresponding grooves on the other side are ofiset laterally in the opposite direction.

In a preferred embodiment of a configurated lamp of the double type wherein the lamp is intended for operation with the grooves facing to the sides, the grooves on one side are displaced down relative to a horizontal plane through the center of the lamp and the grooves on the other side are displaced up to a corresponding extent. By so doing, improved and more rapid stabilization and control of mercury vapor pressure is achieved. In addition, both the lumen maintenance and the loading capacity are increased.

For further objects and advantages, attention is now directed to the following detailed description of an embodiment of the invention and to the accompanying drawing. The features of the invention believed to be novel will be more particularly pointed out in the appended claims.

In the drawing:

FIG. 1 is a side elevation view of a configurated fluorescent lamp embodying a preferred form of the invention, portions of the envelope wall being cut away to shorten the figure and to expose the internal construction.

FIG. 2 is a correspondingly view looking up at the underside of the same lamp.

FIGS. 3 to 7 are transverse sectional views of the lamp at the correspondingly numbered planes with reference to the inverted view of FIG. 2 but drawn to a larger scale.

FIG. 8 is a view of the underside of a fragment of a non phosphor-coated lamp.

Referring to the drawing and more particularly to FIGS. 1 and 2, there is shown a configurated fluorescent lamp of the double groove type comprising an elongated vitreous envelope 1. The envelope is provided with 3 circular or round tube ends Q, 2 which are annularly reduced or shouldered at their extremities for securing thereto bases 3, 3- of the known recessed double-contact type. As shown at the left end of the lamp having the cut away portion, an electrode mount or stem 4 is sealed into each tube end. A pair of lead wires 5 are sealed through the stem and support on their inward projections a filamentary cathode 6. Lateral extensions of the inleads beyond the cathode support a pair of metal plates 7 which serve to trap vaporized or sputtered material from the cathode and also operate as anodes during the positive half cycle of conduction. The outward projections of the lead wires are connected to a pair of contacts located within the projecting boss 8 of the base. The filamentary cathode 6 may consist of a coiled coil of tungsten wire provided with an overwind and coated with an activated mixture of alkaline earth oxides, such as the usual mixture comp-rising barium and strontium oxides.

The lamp contains an ionizable atmosphere including a starting gas or mixture of one or more of the inert rare gases of group of the periodic table at a pressure in the range of 0.5 -tomillimeters of mercury. By way of example, the inert gas filling may consist of argon at 2 to 3 millimeters of mercury, or alternatively a mixture of argon and preferably not over 20% neon at the same pressure. The mercury vapor is provided by a small quantity of mercury exceeding in amount the quantity vaporized during operation of the lamp. During operation, the mercury vapor may exert a partial pressure in the range of 2 to 10 microns, for instance approximately 6 microns for optimum generation of mercury resonance radiation at 2537 A. A phosphor coating on the inside of the envelope converts the 2537 A. radiation into visible light.

The envelope may be described as double grooved, that is it is provided with spaced indentations or re-entrant portions 10, 11 on diametrically opposite sides of the outer wall 12 of generally circular section, giving it a dimpled or crenelated appearance. Otherwise viewed, the indentations r10, 11 may be regarded as short sections of a longitudinal groove alternating on opposite sides of the envelope. The discharge channel cross-section through the grooved sections of the lamp is in general kidney-shaped as illustrated in FIGS. 3 and 7 but it is a kidney-shape which is not symmetrical top and bottom. All the grooves 10 on the facing side of the lamp as seen in FIG. 1 are offset downwardly from a diametral horizontal plane through the lamp, while the grooves 11 on the rear side are offset upwardly. The corresponding cross-sections through the grooves are shown in FIGS. 3

and 7 (inverted). In FIG. 3, the lower rail portion *13 is narrower and more sharply curved than the upper rail portion 14. Correspondingly, in FIG. 7 the lower rail portion 15 is wide and gently curved whereas the upper rail 16 is narrow and sharply curved.

In the intermediate merging zones illustrated progressively in FIGS. 4 to 6, the wall contour changes smoothly from that shown in FIG. 3 to that shown in FIG. 7. In FIG. 4, the right side groove 11a is no longer as deep and the left side groove .100 has begun to form. In FIG. 5 right side and left side grooves 11b, 10b have become substantially equal in depth and a measure of symmetry exists. In FIG. 6 the right side groove 1 1'c has become vestigial while the left side groove 10a is now quite deep and the cross section is so to speak the converse of that of FIG. 4. In all sections, that is in the grooved sections and also in the intermediate merging sections of FIGS. 4 to 6, the discharge is constricted as is desirable for high efliciency at loading.

A feature of the invention is the additional lengthen ing of the are by virtue of the complex zigzag path which it is constrained to follow. In the prior art configurated fluorescent lamps such as that described in Patent 2,950,-

.410, Lemmers et =a1., the discharge channel undulated in a horizontal plane following approximately the center line of the sinuous channel indicated at 17 in FIG. 2; this may be referred to as the primary side-to-side undulation. The present configuration now imparts to the discharge channel an additional vertical undulation according to the dotted line 18 shown FIG. 1, which may be referred to as the secondary up-and-down undulation. The latter undulation may be better appreciated from a consideration of FIGS. 3 to 7 wherein the center of the discharge indicated by the circled X in each moves from position A in FIG. 3, through intermediate positions B, C and D in FIGS. 4 to 6, to the terminal position E in FIG. 7. The transverse locus of the center of the discharge may be represented by the dotted line AB in FIG. 3. The 13013113.]. path is of course the resultant of both undulations but it will be apparent that the eiieotive length of the discharge path has been lengthened. Measurements indicate that the effective lengthening resulting from the additional up and downundulation amounts to about 6% and makes possible an increase in loading in the same percentage without any lowering in overiall eflicency.

The present asymmetrical disposition of all grooves or indentations results in improved mercury vapor pressure control and more rapid stabilization after a period of non-operation. In the configurated lamp of Patent 2,973,- 447, Aicher et aL, two asymmetric grooves only were provided and were located near the longitudinal center of the lamp. Whichever groove happened to have its narrower rail lowermost operated as the mercury vapor pressure control center, and all the excess mercury the lamp eventually collected in the region of that particular narrow the reason being of course that ths rail was the coolest point in the envelope. Although in theory such vapor pressure control should be completely efiective, it was found in practice frequency to be far from perfect. For one thing when the lamp is first installed, the mericury may happen to be collected at one end and a period of time from a few hours up to several hundred hours may be required to achieve migration of all the mercury to the control center. Each time the lamp is turned on after an overnight or longer period of being turned off, appreciable time may again be required to collect the mercury at the control center in order to achieve the desired stabilization. This is particularly apt to occur with long lamps such as 8 foot configurated lamps operating under unfavorable ambient conditions where they are subject to drafits or unbalanced temperature conditions. When a lamp under these conditions is turned 01f, some part of the lamp other than the vapor pressure control center may cool off most rapidly and the mercury vapor tends to migrate to that part and to condense there rather than at the control center. Then when the lamp is subsequently turned on, it will [operate at less than maximum output until such mercury has remigrated back to the pressure control center and this may take up to several hours. Um der conditions of temporary intermittent drafits as may be caused by the opening and closing of doors or windows, it is possible for the lamp never to stabilize so that it never does operate at the maximum output for which it has been designed.

With the present construction, mercury vapor pressure control is much improved and the time to stabilization is greatly reduced. The reason for this is that every groove or indentation which has a narrow lowermost, and this is in fact .every other groove in the lamp, operates a mercury vapor pressure control area. Since these control areas are distributed along the entire length of the lamp, the maximum distance which any mercury has to be displaced in order to arrive and condense at a control area is approximately one bulb or envelope diameter. More eifective control and much more rapid stabilization are thus made possible and actual tests have confirmed it. For example, a lamp with all the grooves asymmetric in accordance with the present invention was placed in a test chamber under controlled ambient conditions involving freedom from drafts and a room temperature of 18 C. The lamp was operated in the usual way with continuous monitoring of wattage input and light output. The lamp wattage stabilized rapidly during the first 20 minutes and did not change appreciably after one hour of operation. After overnight burning of the lamp, the wattage and lumen output were still the same. The lamp was then removed from the set-up and deliberately rotated and turned end for end and then reinstalled. Again after a 29-minute warm up, lamp watts, volts and lumen output had re-established themselves less than 1% of the previous reading. Thus the present invention achieves substantially complete mercury vapor pressure control and stabilization in approximately '20 minutes by comparison with the many hours formerly required after the lamp had been subjected to adverse conditions.

A quite unexpected result of the present invention is an appreciable improvement in lumen maintenance and a pronounced improvement in appearance of the lamp in regards to darkening which becomes observable after a few hundred to a thousand hours of operation. In the prior lamps with the symmetric grooves, the brightness is always =greater near the bottom of the grooves than over the remainder of the periphery. Phosphor depreciation and darkening is directly related to the brightness under operating conditions. The cause and manner of such depreciation is not perfectly understood but it appears to be brought about, at least in part, by atomic attachment of mercury particles to the phomhor surface. Such attachment occurs in proportion to the intensity of the radiation striking the affected phosphor, which in turn is proportional to the intensity of the electric discharge irnr mediately adjacent. With the prior symmetric groove configuration, the discharge is most intense immediately adjacent to the bottom of the grooves. The grooves therefore are brighter in operation but darken more rap idly than the remainder of the lamp envelope. After for instance 1000 hours of operation, the grooves in the prior lamps have a decidedly darker cast than the lamp over all and this of course represents an appearance defect.

With the present asymmetric groove construction, the discharge no longer hugs the bottom of the grooves in the same manner. The envelope Wall, that is the cross section as seen in FIGS. 3 and 7 from the innermost extension of the grooves 10 or 51]. around to the wider rail 14 or 15 starts with a gentle concave curve and progresses smoothly into a convex curve. The more uniform curvature, except in the region of the narrower rail portions 13 or 16 where the intensity of discharge is less, results in a condition where the energy dissipation by charged particles or photons per unit area is substantially uniform throughout the cross-section of the envelope. Also in the intermediate merging or transition zones from one groove to the next, corresponding to FIGS. 4 to 6, the radiant energy striking the envelope walls is likewise substantially uniform throughout. The result is that substantially all parts of the envelope darken at a more uniform rate and excessively rapid darkening of the grooves is eliminated or greatly reduced.

As illustrative of the improvement in lumen main tenance and appearance achieved by the present configuration, in a controlled test, prior art configurated lamps with symmetric grooves had a measured average maintenance of 91% and 85% at 500 hours and 1000 hours of operation respectively. The improved lamps with the asymmetric grooves showed maintenance of 92.5% and 88% at corresponding periods. The improvement in appearance of the new lamp was even more noticeable and quite striking. The prior lamps, especially when unlit, showed decided darkening of the groove bottoms. With the new lamp, no darkening could be observed. Unquestionably there was in fact some darkening with the improved lamp but it occurred substantially uniformly 6 over theentire contour of the envelope so that it could not be observed by mere casual inspection and only became apparent by comparison with a fresh completely undepreciated lamp.

The more uniform phosphor depreciation over the wall contour of the new lamp can readily be shown by operating an uncoated, that is a clear glass lamp without phosphor coating over a comparable period. With a clear lamp, the atomic attachment of the mercury to the envelope wall results in a gradual darkening of the glass which is readily seen by visual observation. With the prior symmetric groove lamps, the bottom and the immediately adjacent curved walls of the groove become much darker than the rest of the bulb after a few hundred hours of operation. With the improved asymmetric groove lamp, the entire envelope contour darkens substantially uniformly except for the narrower rail portion where the mercury condenses and collects. This is shown in FIG. 8 which is an inverted plan view to a larger scale of a fragment of the envelope of a clear, that is non phosphor-coated, lamp. The darkening of the envelope wall, indicated by stippling, is substantially uniform except for the clear area at 19. This area corresponds to a narrow rail 16 (or 13) and remains clear because the discharge does not penetrate into it to any appreciable extent. The invention thus achieves simultaneously improved and more rapid control and stabilization of mercury vapor pressure, an effective increase in length of the discharge path, plus lower depreciation and improved appearance after depreciation.

The increase in elfective length of the discharge path may be taken advantage of to provide higher loading in a given physical length of lamp. Alternatively, it may be taken advantage of in a different way to achieve a lower starting voltage. Both the operating and the starting voltage increase with the depth of the grooves. By pressing in the grooves more deeply, the operating voltage and the loading may be increased but this also causes the starting voltage to rise. There are economic advantages to having as low a starting voltage as possible; this results from the reduction in the open circuit voltage specifications of the ballast required to operate the lamp. With the present improved configurated lamp, the asymmetric rgroove disposition has increased the effective electrical length of the lamp. Therefore the grooves or indentations may now be pressed slightly less deeply and the elfective electrical length along with the loading capacity thereby restored to its original value. However the starting voltage will now have been reduced. Thus the present improvement may be taken advantage of to reduce the starting voltage requirements by approximately 5% in lieu of a gain in loading capacity.

The manufacture of the configurated lamp envelopes may be done by heating a cylindrical glass blank to the softening point in the regions where the grooves or indentations are to be formed, and pressing in the envelope wall to free-form the indentations. During the pressing operation, the cylindrical glass blank is supported in a heated mold with a corresponding semicylindrical cavity therein in which the blank rests. With asymmetric grooves wherein all the grooves are displaced to one side of the center of the lamp, the :glass blank has a tendency to roll or pivot in the mold when the pressing plungers engage it. This is particularly noticeable with long lamps, that is 8 foot long lamps. However a ready solution exists in displacing the grooves to one side over part of the lamp and to the other side over the remainder. For instance in an 8 foot lamp, the grooves may be displaced to the right over the first 4 feet and to the left over the remaining 4 feet of the lamp. The corresponding pattern is also followed on the reverse side of the lamp. This arrangement is just as effective as offsetting all the grooves to one side and solves the problem created by the tendency of the blank to roll or pivot in the mold during the pressing operation.

The specific embodiment of the invention which has been illustrated and described in detail is intended as illustrative and not in order to limit the invention thereto. The scope of the invention is to be determined by the following claims which are intended to cover any modifications coming within its true spirit and scope.

What i claim as new and desire to secure by Letters Patent of the United States is:

1. A low pressure electric discharge lamp comprising a configurated elongated light-transmitting envelope having electrodes sealed into opposite ends and containing an ionizable medium including an inert starting gas and a metal vapor in equilibrium with an excess of nonvaporized metal, said envelope having an outer wall of generally circular section and a plurality of relatively short longitudinally extending grooves alternating on opposite sides of the envelope, said grooves being asymmetrically located relative to a diametral horizontal plane through the longitudinal axis of the envelope, groups of said grooves being ofiset in one direction relative to said plane on one side of the envelope and the corresponding groups on the opposite side being olfset in the opposite direction, whereby to provide improved vapor pressure regulation and control and an increase in the efiective length of the discharge path.

2. A low pressure configurated fluorescent lamp comprising an elongated vitreous envelope coated internally with phosphor, having electrodes sealed into opposite ends, and containing an ionizable medium including an inert starting gas and mercury vapor, said envelope having an outer wall or" generally circular section and a plurality of relatively short longitudinally extending grooves alternating on opposite sides of the envelope, said grooves being asymmetrically located relative to a diarnetral horizontal plane through the longitudinal axis of the envelope, said grooves being offset in one direction relative to said plane on one side of the envelope and in the opposite direction on the other side, whereby to provide improved vapor pressure regulation and control and an increase in the efiective length of the discharge path.

3. A low pressure electric discharge lamp of the double groove type comprising an elongated vitreous envelope having electrodes sealed into opposite ends and containing an ionizable medium including an inert starting gas and mercury vapor in equilibrium with an excess thereof during normal operation, said envelope having an outer Wall of generally circular section and a plurality of relatively short longitudinally extending grooves alternating on opposite sides of the envelope, substantially all of said grooves being asymmetrically located relative to a hori zontal diametral plane through the longitudinal axis of the envelope, substantial groups of grooves being oltset below said diametral plane on one side of the lamp and above said plane on the opposite side of the lamp whereby to provide in the former case a narrower rail below and a wider rail above, and in the latter case a wider rail below and a narrower rail above said diametral plane.

4. A low pressure configurated fluorescent lamp of the double groove type comprising an elongated vitreous envelope coated internally with phosphor and having electrodes sealed into opposite ends and containing an ionizable medium including an inert starting gas and mercury vapor in equilibrium with an excess thereof during normal operation, said envelope having an outer wall of generally circular section and a plurality of relatively short longitudinally extending grooves alternating on opposite sides of the envelope, substantially all of said grooves being asymmetrically located relative to a horizontal di metral plane through the longitudinal axis of the envelope, substantial groups of grooves being offset below said diametral plane on one side of the lamp and above said plane on the opposite side of the lamp whereby toprovide in the former case a narrower rail below and a wider rail above, and in the latter case a wider rail below and a narrower rail above, the discharge plasma in each grooved portion being thereby displaced toward the wider rail and away from the narrower rail and resulting in a lower operating temperature for the narrower rails located below said diametal plane which thus serve as mercury vapor pressure control centers distributed along the length of the lamp.

5. A. low pressure configurated fluorescent lamp of the double groove type comprising an elongated vitreous envelope coated internally with phosphor, having electrodes sealed into opposite ends, and containing an ionizable medium including an inert starting gas and mercury vapor in equilibrium with an excess thereof during operation, said envelope having an outer wall or" generally circular section and a plurality of relatively short longitudinally extending grooves alternating on opposite sides, all of said grooves being asymmetrically located relative to a horizontal diametral plane through the longitudinal axis of said envelope, a group of grooves on one side of the lamp being oifset below said diametral plane and a corresponding group on the other side being ofiset above said diametral plane, the offset of said grooves providing a wider rail portion on one side and a narrower rail portion on the other side, said wider rail portion having throughout a gently curved well contour to assure substantially uniform exposure to. radiant effects per unit area of the envelope whereby to achieve substantially improved maintenance and avoid non-uniform darkening of the envelope wall, said asymmetric grooves providing further an up and down undulation ofthe discharge channel simultaneously with a side to side undulation whereby to achieve a greater effective electrical length and higher loading capacity, said narrower rail portions providing mercury vapor pressure control centers distributed along the length of the envelope for improved mercury vapor pressure control and regulation along with more rapid stabilization.

References Cited in the file of this patent UNITED STATES PATENTS Lemmers et a1. Aug. 23, 1960 Aicher et al Feb. 28, 1961 

1. A LOW PRESSURE ELECTRIC DISCHARGE LAMP COMPRISING A CONFIGURATED ELONGATED LIGHT-TRANSMITTING ENVELOPE HAVING ELECTRODES SEALED INTO OPPOSITE ENDS AND CONTAINING AND IONIZABLE MEDIUM INCLUDING AN INEER STARTING GAS AND A METAL VAPOR IN EQUILIBRIUM WITH AN EXCESS OF NONVAPORIZED METAL, SAID ENVELOPE HAVING AN OUTER WALL OF GENERALLY CIRCULAR SECTION AND A PLURALITY OF RELATIVELY SHORT LONGITUDINALLY EXTENDING GROOVES ALTERNATING ON OPPOSITE SIDES OF THE ENVELOPE, SAID GROOVES BEING ASYMMETRICALLY LOCATED RELATIVE TO A DIAMETRAL HORIZONTAL PLANE THROUGH THE LONGITUDINAL AXIS OF THE ENVELOPE, GROUPS OF SAID GROOVES BEING OFFSET IN ONE DIRECTION RELATIVE TO SAID PLANE ON ONE SIDE OF THE ENVELOPE AND THE CORRESPONDING GROUPS ON THE OPPOSITE SIDE BEING OFFSET IN THE OPPOSITE DIRECTION, WHEREBY TO PROVIDE IMPROVED VAPOR PRESSURE REGULATION AND CONTROL AND AN INCREASE IN THE EFFECTIVE LENGTH OF THE DISCHARGE PATH. 